Speaking from memory is an ancient public speaking tradition referred to as oratory. In this style of speaking, you prepare the speech in the manuscript form as just described but then commit the words to memory.

Oratory delivery is fairly uncommon today as a form of public speaking, as it is both time-consuming and risky. A speaker who forgets a word or phrase can easily lose his or her place in the speech, panic, and never recover. But even if every line is delivered perfectly, the very nature of memorization can create a barrier between speaker and audience. Having memorized the speech and rehearsed without an audience, the speaker tends to deliver it as if the audience wasn’t there. Such a speech can therefore end up feeling more like a performance, a one-man or one-woman show, rather than a communication that engages with the audience.